The present invention relates to a novel tetrahydropyran-5-one compound useful as an intermediate for the synthesis of various organic compounds, e.g. those used as a flavor. In particular, the present invention relates to a 2-hydrocarbyloxy- or 2-acyloxy-3,4-dihalogeno-6-hydrocarbyl-tetrahydropyran-5-one compound.
2-Alkyl-3-hydroxy-4H-pyran-4-one compounds, e.g. 2-methyl-3-hydroxy-4-pyrone, which is called maltol, are important organic compounds useful as a flavoring material in foods and stock feeds with increasing demand in recent years. No convenient synthetic methods have been known for the preparation of maltol. Conventionally, according to a fermentative method, kojic acid obtained by fermentation is converted into the objective compound through four steps including oxidation and decarboxylation. This process is disadvantageous due to the lengthy sequence of the steps taking about one week for the fermentation as well as due to the necessity of large-scaled facility for the fermentation step, precious metal catalyst in the oxidation step and a high temperature of 250.degree. C. or higher in the decarboxylation step.
On the other hand, a synthetic method for the preparation of maltol is disclosed in Japanese Patent Disclosure No. 52-31077 starting with a 2-furyl carbinol compound. The method comprises the steps of an electrolysis or reaction of the 2-furyl carbinol compound with a halogen as dissolved in an alcohol to introduce alkoxy groups to the 2- and 5-positions of the furan ring, reaction of a strong organic acid with the 2, 5-dialkoxy furyl derivative above obtained to the formation of a 5,6-dihydro-2H-pyran-5-one derivative, epoxidization of the above compound at the 3- and 4-positions, and finally a rearrangement reaction of the epoxy compound to the objective compound.
The above-described synthetic method is also disadvantageous due to the length of the reaction steps as well as due to the danger of explosion resulting from the use of a peroxide, such as hydrogen peroxide, in the epoxidization step. Such danger may be avoided only by carrying out the reaction at a relatively low temperature at the sacrifice of reaction velocity.
The compounds of the present invention have been discovered as an intermediate compound in the course of extensive investigations undertaken by the inventors to establish a novel and advantageous route for the synthetic preparation of 2-alkyl-3-hydroxy-4H-pyran-4-one compounds including maltol.